The phase space structure in the vicinity of vertical Lyapunov orbits around L1,2 in a barred galaxy model

Abstract

ABSTRACT We study the phase space structure and the orbital diffusion from the vicinity of the vertical Lyapunov periodic orbits around the unstable Lagrangian points L1,2 in a 3D barred galaxy model. By perturbing the initial conditions of these periodic orbits, we detected the following five types of orbital structures in the 4D spaces of section: (i) Ring-like structures, sticky for large time intervals to the unstable invariant manifolds of the simple and double unstable vertical Lyapunov periodic orbits. (ii) 2D tori belonging to quasi-periodic orbits around stable periodic orbits existing in the region. They are associated either with vertical stable periodic orbits around L4,5 or with ‘stable anomalous’ periodic orbits. (iii) Orbits sticky for large time intervals to these tori, forming ‘sticky tori’, before they slowly depart from them. (iv) Clouds of points that have a strong chaotic behaviour. Such clouds of consequents have slow diffusion speeds, because they are hindered by the presence of the tori around the ‘stable anomalous’ periodic orbits. (v) Toroidal zones consisting of points that stick for long time on the unstable invariant manifolds of the ‘unstable anomalous’ periodic orbits. By continuing the integration, we find that eventually they become strongly chaotic, retaining however small diffusion speeds, due to the presence of the tori around the stable anomalous periodic orbits.